Aromatic polycarbonates belong to the group of engineering thermoplastics. They are distinguished by the combination of the properties transparency, heat resistance and toughness which are significant in engineering applications.
High molecular weight linear polycarbonates are obtained by the phase boundary process by reacting the alkali metal salts of bisphenols with phosgene in the two-phase mixture. Molecular weight may be controlled by the quantity of monophenols, such as for example phenol or tert.-butylphenol. These reactions virtually exclusively yield linear polymers. This may be demonstrated by end group analysis.
With regard to the production of linear polycarbonates by the phase boundary process, reference is made by way of example to H. Schnell, Chemistry and Physics of Polycarbonates, Polymer Reviews, vol. 9, Interscience Publishers, New York 1964 p. 33 et seq. and to Polymer Reviews, vol. 10, “Condensation Polymers by Interfacial and Solution Methods”, Paul W. Morgan, Interscience Publishers, New York 1965, chapter VIII, p. 325.
U.S. Pat. No. 4,185,009, DE A 25 00 092 and JP B 79039040 describe a process in which, starting from mixtures of specific bisphenols with chain terminators and isatin bisphenols as branching agents, branched, high molecular weight polycarbonates may be obtained after reaction with phosgene in a phase boundary reaction. DE A 42 40 313 describes copolycarbonates with improved flowability based on bisphenol A and bisphenol TMC with isatin biscresol as branching agent.
DE A 19 913 533 describes highly crosslinked polycarbonates, the production of which involves the use of oligomeric or polymeric branching agents. DE A 19 943 642 mentions branched polycarbonates which, by virtue of their pseudoplasticity, are suitable for use as a water bottle material.
U.S. Pat. No. 5,367,044 accordingly describes bottles made from branched polycarbonate, in which 1,1,1-tris-(4-hydroxyphenyl)ethane (THPE) is used as the branching agent in quantities of 0.28-0.36 mol %.
Because of their better flowability in comparison with linear polycarbonates, branched polycarbonates are especially of interest for applications in which good flow of the polymer melt at relatively high shear rates is desired, i.e. for example when injection molding complex structures. Branched polycarbonates are distinguished by pseudoplasticity and can no longer be considered Newtonian fluids.
In the prior art, high purity trifunctional products are used as branching agents. It would be advantageous to use trifunctional compounds which can be produced straightforwardly and contain only bisphenols as secondary components, which do not require troublesome separation.